Paspalum setaceum (Hairy Beadgrass)
|Also known as:||Hairy Lens Grass, Thin Paspalum, Slender Paspalum|
|Habitat:||part shade, sun; open, sandy soil; savanna, roadsides, woodland edges, disturbed soils|
|Fruiting season:||July - September|
|Plant height:||15 to 40 inches|
|Wetland Indicator Status:||GP: FAC MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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1 to 3 (rarely more) spreading to ascending spike-like racemes, at the tip of the stem and arising singly or in pairs from the upper leaf axils. Sometimes all or part of a raceme is hidden, tucked inside the leaf sheath. Racemes are up to 5 inches long with a flat, ribbon-like central stalk (rachis). Dozens of spikelets (flower clusters) are arranged in two rows along the rachis, usually in pairs and often crowded. Spikelets are short-stalked, 1.4 to 2.6 mm long, round to oval with a slightly pointed tip, flattened on one side like a split pea, and each with a single fertile, perfect floret (both male and female parts) and one sterile floret.
Grass spikelets typically have a pair of glumes (bracts) at the base of a spikelet, but the lower glume is absent or obscure on this species. The upper glume is thin, light green, as long and as wide as the spikelet, smooth to minutely hairy, and 3-veined. The lower floret is sterile surrounded by a pair of bracts (lemma and palea), the lemma thin and about the same size as the upper glume, with or without a distinct midvein, and the palea absent or obscure. The upper floret is fertile, the lemma and palea both thicker than the glume, round to elliptic with edges curled around the floret (see mature fruit photo below).
Leaves and stems:
Leaves are crowded on the lower part of the stem with a few more widely spaced above. Leaves are flat, erect to floppy, up to 10 inches long and about ½ inch wide or less. Depending on the variety, color is yellowish-green or light to dark green, and surfaces and edges are variably covered in short, soft hairs and/or long, spreading hairs.
The sheath is open, the edges with a fringe of hairs and overlapping in the front at or near the tip. Depending on the variety, the sheath surface is hairless or variably covered in long, spreading hairs. The ligule (membrane where the leaf joins the sheath) is short and membranous with a band of white hairs behind it. Nodes are hairless. Stems are hairless and mostly erect, sometimes spreading, forming clumps of a few to several stems from short rhizomes.
As spikelets mature the glume and sterile lemma become papery but the fertile lemma and palea harden, locking the grain (seed) inside. Spikelets turn straw-colored to light brown with age, the entire spikelet falling off at the tip of its short stalk, leaving a naked rachis behind.
Paspalum is a large genus, with at least 65 species in North America, though taxonomy is more than a little confusing. Fortunately, P. setaceum is the only one of this genus in Minnesota and nothing else in the state looks quite like it. Unfortunately, there are as many as 9 varieties, not all of which are universally recognized, with some references treating some of these as separate species and others lumping them all together with no vars. Variable traits are leaf width and color, degree of hairiness and whether hairs are long or short, whether the sterile lemma has a distinct midvein, and whether stems are mostly erect or not. Of the 2 varieties recognized in Minnesota, var. muhlenbergii is the more common, distinguished by green leaves up to ½ inch wide that are more or less evenly covered in long, spreading hairs, and spikelets with a distinct midvein on the sterile lemma. By contrast, var. stramineum has yellowish-green leaves not more than ¼ inch wide that are short-hairy with few long hairs (if any), and the sterile lemma lacks the midvein. Both are said to grow more or less erect. Based on the leaf hairs all of our images should be var. muhlenbergii, but we have yet to see a distinct midvein on any population we've encountered, except perhaps on just 1 or 2 spikelets out of an entire raceme. We'll be on the lookout for it.
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- Hairy Beadgrass plant
- Hairy Beadgrass plants
- Hairy Beadgrass plants
- leaf hairs, var. muhlenbergii
- more spikes
- flowering stems are not always erect
Photos by K. Chayka taken in Anoka and Ramsey counties. Photos courtesy Peter M. Dziuk taken in Dakota and Wabasha counties.
Have you seen this plant in Minnesota, or have any other comments about it?